Gyretes Brullé (Coleoptera: Gyrinidae) from Brazil: Morphology of eggs and early instars

Abstract

Taxonomic information regarding Gyrinidae is mostly based on adults, especially due to the difficulty in collecting immatures and assigning them to a particular species. Association between immatures and adults is sometimes difficult because closely related species can be found in the same habitat. To solve this problem a feasible technique is rearing under laboratory conditions. However, this method is challenging because larval survival rate is usually low, and emulation of natural conditions is difficult. Molecular techniques, especially the use of the COI gene, have been applied to identify species and to associate different life stages. However, in some species groups this marker has not been successful in distinguishing closely related species. The objectives of this study are to describe the egg and the first two instars of Gyretes nubilus Ochs, 1965 and the egg of G. minax Ochs, 1967 and to evaluate the utility of COI to associate immatures and adults. The association of these immature stages with adults was done either rearing adults under laboratory conditions or by using DNA sequence data (COI), corroborating the utility of this molecular marker to associate immature and adults in Gyretes. These immature stages are described, including chaetotaxic analysis of larvae for the first time for the genus Gyretes Brullé, 1835. The eggs are described based on scanning electron microscopy. The eggs are similar to those of other Gyrinidae genera in having a micropylar region in the anterior pole and a longitudinal fissure, and by the absence of an aeropyle, but they differ mainly in characters related to chorionic structure and reticulation. Larvae of Gyretes can be distinguished from those of the other Neotropical Gyrinidae genera by a combination of several characters, including the frontoclypeal seta FR3 short, presence of three conspicuous additional setae on lateral region of parietal (contiguous to stemmata), and posterior margin of lacinia smooth, with apex not indented.

Burmese amber reveals a new stem lineage of whirligig beetle (Coleoptera: Gyrinidae) based on the larval stage

“…In terms of plesiomorphic features, the form of TI7 is spine like, similar to that seen in other adephagan larvae, such as Haliplidae, Aspidytidae, Meruidae and several Dytiscidae (Nilsson, 1988;Van Vondel, 2005;Alarie & Bilton, 2005, 2011Michat et al, 2014aMichat et al, , 2017a, whereas the known gyrinid larvae have TI7 hair like in form (Michat et al, 2010(Michat et al, , 2017bMichat & Gustafson, 2016;Colpani et al, 2018). Similarly plesiomorphic is the position of TA1 being not only situated at mid-length on the tarsus [a condition seen only in the larvae of Dineutus (Michat et al, 2017b) and in some Gyretes (Colpani et al, 2018)], but also dorsally as in other adephagan beetles (Nilsson, 1988;Alarie et al, 2004;Alarie & Michat, 2014;Michat et al, 2014bMichat et al, , 2017aUrcola et al, 2019) [unlike Gyretes and, to a lesser degree, Dineutus, where TA1 is situated laterally (Michat et al, 2017b;Colpani et al, 2018)]. Most gyrinid larval genera have TA1 positioned apically, representing a derived condition (Archangelsky & Michat, 2007;Michat et al, 2010Michat & Gustafson, 2016).…”

“…In our amber specimen and other adephagan larvae (Nilsson, 1988) TA1 is situated at mid-length on the dorsal surface of the tarsus (Fig. 5A), whereas all other known gyrinid larvae, with the exception of Dineutus and some Gyretes, have TA1 positioned distally towards the tibial apex (Crespo, 1986b;Michat et al, 2010Michat et al, , 2017bColpani et al, 2018). 38.…”

“…Terminology follows previous papers dealing with the larval morphology of Gyrinidae (Archangelsky & Michat, 2007;Michat et al, 2010Michat et al, , 2017bMichat & Gustafson, 2016;Colpani et al, 2018). The following abbreviations are used: AN, antennae; CO, coxa; FE, femur; FR, frontoclypeus; LA, labium; MN, mandible; MX, maxilla; PA, parietal; PT, pretarsus; TA, tarsus; TI, tibia; TR, trochanter.…”

“…Setae were coded using the two capital letter abbreviations corresponding to the structure on which they were located in addition to a number. Chaetotaxic coding was done in comparison to the primary chaetotaxy of prior studies on larvae of Gyrinidae (Archangelsky & Michat, 2007;Michat et al, 2010Michat et al, , 2017bMichat & Gustafson, 2016;Colpani et al, 2018) and other adephagans (Bousquet 2005(Bousquet , 2011Alarie & Michaet, 2014;Michat et al, 2014aMichat et al, , b, 2017aUrcola et al, 2019). Homology of setae was established via similarity of position (Wiley, 1981).…”

“…The larvae of several extant gyrinid genera remain unknown, including key taxa, such as Spanglerogyrus Folkerts, 1979 andHeterogyrus Legros, 1953, representing the subfamilies Spanglerogyrinae and Heterogyrinae (Miller & Bergsten, 2012), and for some genera in the subfamily Gyrininae, such as the dineutine genus Porrorhynchus Laporte, 1835 and the gyrinine genus Metagyrinus Brinck, 1955 (Michat et al, 2017b). Recent efforts have been made not only to describe the general larval morphology of different gyrinid genera formally, but also to provide a formal system of chaetotaxy, allowing chaetotaxic analysis and improved homology across larval characters for use in future phylogenetic studies (Archangelsky & Michat, 2007;Michat et al, 2010Michat et al, , 2017bMichat & Gustafson, 2016;Colpani et al, 2018).…”